(1) Field of the Invention
This invention relates to new liquid-crystal compounds and to liquid crystal compositions containing the same, particularly smectic liquid crystal compositions.
The liquid-crystal compounds herein include those compounds which are useful as a component of liquid crystal compositions even though they do not exist in the form of liquid crystal.
(2) Description of the Related Art
Twisted nematic (TN) and dynamic scatter (DS) types, both employing nematic liquid crystal cells, are the modes of liquid-crystal display most extensively used at present. One disadvantage of conventional nematic liquid crystal cells is low response speeds (on the order of milliseconds at the highest), which limit the use of this type of liquid crystal cells.
It has recently been found that higher response speeds can be achieved by smectic liquid crystal cells and that some of optically active smectic compounds are ferroelectric. The ferroelectric liquid crystals are a group of compounds which are ferroelectric when they exist as chiral smectic C (hereinafter abbreviated as "SmC*") phase and are typified by 2-methylbutyl 4-(4-n-decyloxybenzylideneamino)cinnamate (hereinafter abbreviated as "DOBAMBC") of the following structural formula [J. Physique, 39, L-69 (1975)], ##STR2##
More recently N. A. Clark et al. [Appl. Phys. Lett., 36, 89 (1980)] found that very high response speeds on the order of microseconds can be achieved by thin-film DOBAMBC cells. Since then ferroelectric liquid crystals have been receiving attention not only as a material for display in liquid-crystal TV sets, but also as an element for optoelectronics devices (e.g., photo printer heads, optical Fourier transformation elements, and light valves).
DOBAMBC remains ferroelectric only within a relatively narrow temperature range, and is unsatisfactory in physical and chemical stability because it is a Schiff base. Hence there has been a great demand for new ferroelectric compounds which are stable both physically and chemically, remain ferroelectric over a wide temperature range, have large dielectric constant, and can be driven at a low voltage.